Methods for making a low inertia laminated rotor

ABSTRACT

A rotor assembly having a plurality of rotor plates mounted to a shaft, and methods of construction for a rotor assembly are disclosed. Each rotor plate in the assembly may be provided with a central opening extending between the first and second sides through which the shaft extends. In one aspect, the rotor plates are provided with a plurality of lobes extending away from the central opening, wherein each of the lobes has a lobe opening extending through the thickness of the plates. In one embodiment, the rotor plates are rotationally stacked to form a helical rotor.

RELATED APPLICATIONS

This application is being filed on Mar. 11, 2015, as a PCT International Patent application and claims priority to U.S. Patent Application Ser. No. 61/951,788 filed on Mar. 12, 2014, the disclosure of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

This present disclosure relates to rotor assemblies that may be utilized in rotary equipment applications, for example, volumetric expansion and compression devices.

BACKGROUND

Rotors are a commonly used in applications where it is desirable to compress or move a fluid and where it is desired to remove energy from the fluid. In one example, a compressor or supercharger utilizes a pair of rotors to increase airflow into the intake of an internal combustion engine. In another example, a volumetric fluid expander includes a pair of rotors that expand a working fluid to generate useful work at an output shaft. In such applications, it is known to provide machined or cast rotors having a unitary construction with a solid cross-sectional area. Improvements are desired.

SUMMARY

The disclosure is directed to a rotor assembly comprising a plurality of rotor plates mounted to a shaft. In one aspect, each of the rotor plates has a first side and a second opposite side separated by a first thickness. Each rotor plate may also be provided with a central opening extending between the first and second sides through which the shaft extends. In yet another aspect, the rotor plates are provided with a plurality of lobes extending away from the central opening, wherein each of the lobes has a lobe opening extending between the first and second sides. The plurality of rotor plates are stacked and secured together to form the rotor assembly such that at least one of the first and second sides of one rotor plate is adjacent to and in contact with at least one of the first and second sides of another rotor plate. In one embodiment, the rotor plates are stacked directly upon each other such that the entirety of one side of one rotor plate is entirely covered by an adjacent rotor plate. In one embodiment, the rotor plates are rotationally stacked to form a helical rotor such that one rotor plate does not entirely cover the adjacent rotor plate. The disclosure also includes a volumetric fluid expander and a compressor or supercharger including a pair of the above described rotors.

The disclosure also is directed to a process for making a laminated rotor assembly. In one step of the process a plurality of rotor plates are provided in accordance with the above description. In one step, the rotor plates are stacked together to form either a straight rotor or a helical rotor. In one step, the rotor plates are secured together, for example by welding. In one step, the rotor is mounted to a shaft to form the laminated rotor assembly. The shaft may be burred to better engage the shaft with the stacked rotor plates. The process may also include applying an abradable coating to the rotor as well.

In one embodiment, each of the rotor plates may also be provided with a first indexing feature configured to align with a second indexing feature on a mandrel. In such a configuration, a second process for constructing the laminated rotor assembly may include the steps of providing a plurality of rotor plates having the first indexing feature and providing a mandrel having the second indexing feature. In one step of the second process, the rotor plates are stacked onto the mandrel such that the mandrel extends through the central opening of each plate and such that each rotor plate first indexing feature is aligned with the mandrel second indexing feature. In one embodiment, the second indexing feature extends along the length of the mandrel and is parallel to the longitudinal axis of the mandrel such that a straight rotor will be formed. In one embodiment, the second indexing feature extends along the length of the mandrel and has a helical shape such that a helical rotor will be formed.

In one step of the second process, the rotor plates are secured together, for example, by welding. In one step of the second process, the mandrel is removed from the rotor plates. In one embodiment, an extraction tool is provided that presses the mandrel out of the assembled rotor plates. In one step of the second process, a shaft which may be provided with burrs is inserted into the central openings of the rotor plates to form the rotor assembly. As with the first process, an abradable coating may be applied to the assembled rotor in the second process. In one step of the second process, balancing holes may be provided, for example by drilling holes into the stacked rotor plates, to rotationally balance the rotor assembly.

The above features and advantages and other features and advantages of the present teachings are readily apparent from the following detailed description of the best modes for carrying out the present teachings when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a low inertia laminated rotor assembly in accordance with the principles of the present disclosure.

FIG. 2 is a top view of a rotor plate usable in the rotor assembly shown in FIG. 1.

FIG. 3 is a side view of the rotor plate shown in FIG. 2.

FIG. 4 is a top view of a rotor plate usable in the rotor assembly shown in FIG. 1.

FIG. 5 is a top view of a rotor plate usable in the rotor assembly shown in FIG. 1.

FIG. 6 is a perspective view of the unitary rotor with the shaft removed.

FIG. 7 is a perspective view of a shaft onto which the rotor plates of FIGS. 2-5 may be mounted.

FIG. 8 is an end view of the shaft shown in FIG. 7 in a die forming process.

FIG. 9 is a schematic showing a process for producing a laminated rotor.

FIG. 10 is a schematic view of a vehicle having a fluid expander and a compressor in which rotor assemblies of the type shown in FIG. 1 may be included.

FIG. 11 is a schematic showing a second process for producing a laminated rotor.

FIG. 12 is a perspective view of a rotor assembly apparatus that may be used in the second process for producing a laminated rotor shown at FIG. 10.

FIG. 13 is a perspective view of the rotor assembly apparatus shown in FIG. 12 with a rotor plate aligned with the mandrel.

FIG. 14 is a perspective view of the rotor assembly apparatus shown in FIG. 12 with a rotor plate aligned with the mandrel.

FIG. 15 is a perspective view of the rotor assembly apparatus shown in FIG. 12 with a rotor plate aligned with the mandrel and with a rotor plate mounted about the mandrel.

FIG. 16 is a perspective view of the rotor assembly apparatus shown in FIG. 12 with two rotor plates mounted about the mandrel.

FIG. 17 is a perspective view of the rotor assembly apparatus shown in FIG. 12 with a plurality of rotor plates mounted about the mandrel to form a completed rotor.

FIG. 18 is a perspective view of the rotor and rotor assembly apparatus shown in FIG. 17 with an additional base portion secured to the assembly such that the rotor plates can be secured together to form a unitary rotor.

FIG. 19 is a perspective view of the completed rotor with the base portions removed from the mandrel and with the plates secured to each other.

FIG. 20 is a perspective view of the unitary rotor and mandrel mounted in a mandrel extraction tool.

DETAILED DESCRIPTION

Various embodiments will be described in detail with reference to the drawings, wherein like reference numerals represent like parts and assemblies throughout the several views. Reference to various embodiments does not limit the scope of the claims attached hereto. Additionally, any examples set forth in this specification are not intended to be limiting and merely set forth some of the many possible embodiments for the appended claims. Referring to the drawings wherein like reference numbers correspond to like or similar components throughout the several figures.

Rotor Construction

Referring to FIG. 1, a complete laminated rotor assembly 5 is presented. As shown, laminated rotor 30 includes a plurality of stacked rotor plates 200 that are mounted to a common shaft 38. In the embodiment shown, the rotor plates 200 are rotationally stacked such that the rotor assembly 30 has a helical rotor having a constant helix angle. By use of the term “rotationally stacked,” it is meant that the plates are rotationally offset with respect to each other such that one rotor plate does not entirely cover an adjacent rotor plate. The laminated rotor 30 can also be provided as a straight rotor by stacking the rotor plates 200 such that adjacent plates 200 completely cover each other.

Examples of a rotor plate 200 are shown at FIGS. 2-5. As shown, rotor plate 200 has three radially spaced lobes 202-1, 202-2, 202-3 (collectively referred to as lobes 202) extending away from a central axis X to a respective tip portion 203-1, 203-2, 203-2 (collectively tips 203). In one aspect, the lobes 202 have or define a convex outline and the root portions 204 have or define a concave outline that together define an outer perimeter 206 of the rotor plate 200.

As shown, the lobes 202 are equally spaced apart by adjacent root portions 204-1, 204-2, 204-3 (collectively referred to as root portions 204) at a first separation angle a1. In the embodiment shown, the separation angle a1 is about 120 degrees. Although three lobes are shown, it should be understood that fewer or more lobes may be provided with corresponding separation angles, for example, two lobes with a separation angle of 180 degrees, four lobes with a separation angle of 90 degrees, five lobes with a separation angle of 72 degrees, and six lobes with a separation of 60 degrees. When stacked together to form a rotor 30, the central axis X of each rotor plate 200 is coaxial with axis X1, X2, respectively.

Each rotor plate 200 also has a first side 208 and a second side 210 separated by a first thickness t1. In one embodiment, the thickness t1 is about 0.25 millimeters (mm). However, it should be noted that other thicknesses may be used, for example, thicknesses between about 0.1 mm and about 1 mm and between about 0.1 mm and about 0.5 mm. Each plate 200 is also shown as being provided with a central opening 212 extending between the first and second sides 208, 210, wherein the central opening 212 is centered on the central axis X.

An indexing feature 214 may also be provided adjacent to or as part of the central opening 212. In the embodiment shown, the indexing feature 214 includes three radially spaced notches 214-1, 214-2, and 214-3 that are respectively aligned with the lobes 202-1, 202-2, and 202-3. As discussed in greater detail with respect to rotor assembly method 2000, the indexing feature 214 allows the rotor plates 200 to be aligned relative to one another during the stacking or assembly process. Although three notches are shown for the indexing feature 214, it should be understood that more or fewer notches or other features capable of performing an alignment function may be provided, such as tabs extending towards the center of the central opening 212.

With reference to the rotor plate 200 shown at FIG. 2, it can be seen that the lobes 202 are entirely solid material such that the only opening that extends through the thickness t1 of the rotor is the central opening 212. This type of lobe may be referred to as a solid lobe and a rotor plate having such lobes may be referred to as a solid-lobe rotor plate. However, the rotor plate 200 may be provided with one or more openings within each lobe. This type of lobe may be referred to as a hollow lobe and a rotor plate having such lobes may be referred to as a hollow-lobe rotor plate.

Referring to FIG. 4, an example of a hollow-lobe rotor plate 200 is shown in which each lobe 202 is provided with a respective opening 205-1, 205-2, 205-3 (collectively openings 205). In one aspect, each opening 205 has an area that is the majority of the surface area of the lobe 202, as defined by the outer perimeter of the lobe 202. In one aspect, the total opening area defined by the openings 205 and the central opening 212 is greater than the total area defined by the outer perimeter 206 of the rotor plate 200. In one aspect, the openings 205 are configured such that the remaining material of the lobe 202, adjacent the outer perimeter 206 and proximate the tip portion 203, has a generally constant width w1. Near the root portions 204, the material width is shown as being increased from the first width w1 for greater strength.

In the embodiment shown at FIG. 4, the total opening area of the openings 205 and central opening 212 is about 50% of the total area defined by the outer perimeter 206 resulting in a rotor plate 200 that has about 50% less material, as compared to a solid-lobe rotor with the same central opening size. The size and configuration of the openings 205 in the rotor plate 200 can be configured to result in a total opening area ranging from 0% to 70% of the total perimeter area, and preferably between about 30% and about 60% of the total perimeter area. Stated in other terms, the size and configuration of the openings 205 in the rotor plate 200 can be configured to result in a total material reduction ranging from 0% to about 70%, and preferably between about 30% and about 60% of the total perimeter area.

The provision of an opening 205 in the lobe 204, as shown in FIG. 4, substantially reduces the amount of material required to form the rotor 30. Accordingly, the weight of the rotor plate 200, and thus the weight of the rotor 30 is significantly less as compared to a solid rotor or a laminated rotor using solid-lobe plates. As importantly, the moment of inertia or rotational inertia of the rotor plate 200, and thus the assembled rotor 30, is substantially reduced as compared to a solid material rotor. In the embodiment shown, the rotational inertia of the rotor plate 200 and rotors 30 is about 45% less than a solid rotor made of the same material and having the same geometric configuration. The size and configuration of the openings 205 in the rotor plate 200 can be configured to result in a reduction of rotational inertia, as compared to a solid rotor, ranging from 0% to about 45% and preferably between about 25% to 55%. Although the rotor plate 200 shown in FIGS. 4 and 5 is shown with one opening 205 in each lobe 202, more than one opening may be provided in each lobe as desired, for example, two, three, or four openings 205 in each lobe 202.

With reference to FIG. 5, the openings 205-1, 205-2, 205-3 are provided as smaller circular openings that can be used for the purpose of determining the geometric center of the rotor plate 200 during assembly. The holes 205-1, 205-2, 205-3 allow for the center of the rotor lobe to be accurately identified and indexed in a machining process after assembly of the rotor 30. Where holes 205-1, 205-2, 205-3 are provided, an indexing tool can then be used that references the holes 205-1, 205-2, 205-3 for the machining process.

As the mass of the rotor 30 is reduced when constructed from at least some hollow-lobe rotor plates 200, the rotor plates 200 can be made from a material that is sufficient to maintain structural integrity under high temperature and loads, such as would be the case where a volumetric fluid expander 20 (discussed later) having rotor assemblies 5 receives direct exhaust from an internal combustion engine. In some examples, each of the rotor plates 200 is fine blanked, stamped, or laser or water jet cut from a thin sheet of metal, such as stainless steel, carbon steel or aluminum. The material can be pre-coated using a silk screen process with copper or nickel.

Rotor Assembly Method 1000

Referring to FIG. 9, an example of a rotor assembly system and process 1000 in accordance with the disclosure is presented. It is noted that although the figures diagrammatically show steps in a particular order, the described procedures are not necessarily intended to be limited to being performed in the shown order. Rather at least some of the shown steps may be performed in an overlapping manner, in a different order and/or simultaneously. Also, the process shown in FIG. 8 is exemplary in nature and other steps or combinations of steps may be incorporated or altered without departing from the central concepts disclosed herein.

In a step 1002, a plurality of rotor plates 200 in accordance with the above description are provided. In a step 1004, each of the provided rotor plates 200 is stacked such that at least a portion of one of the rotor plate sides 208, 210 is adjacent and in contact with another rotor plate side 208, 210. In the embodiment shown, the sides 208, 210 of each rotor plate 200 are completely planar such that, when stacked, no gap exists between adjacent rotor plates. As presented, each rotor plate 200 is slightly offset from the adjacent rotor plate about the central axis X to form a helical rotor 30.

It is noted that many configurations of stacked rotor plates 200 are possible using assembly method 1000. In the example embodiment shown, the stack could include closed-lobe rotor plates with indexing holes of the type shown in FIG. 5 at each end with hollow-lobe rotor plates of the type shown in FIG. 4 there between. In another embodiment, the stack could consist entirely of hollow-lobe rotor plates of the type shown in FIG. 4. Alternatively, the stack could include closed-lobe rotor plates of the type shown in FIG. 2 at each end with hollow-lobe rotor plates of the type shown in FIG. 4 there between. In even yet another configuration, the stack could include alternating hollow-lobe rotor plates with solid-lobe rotor plates. Alternatively, the stack could include a majority of the plates as being hollow-lobe rotor plates with solid-lobe rotor plates being inserted incrementally throughout the stack, for example, every tenth plate could be a solid-lobe rotor plate with the remaining plates being a hollow-lobe type.

In a step 1006, the rotor plates 200 are secured together. The stacked rotor plates 200 can be secured together, for example by welding. In one example, the plates 200 are secured together by laser welding. In another example, the rotor plates 200 can be welded together in a vacuum or continuous belt furnace. In an alternative, the plates 200 can be plated and resistive-welded together. In one embodiment, the rotor plates 200 are secured with welds that extend along the rotor plate tips 203 and along each side of the rotor lobes 202 for a total of nine helical welds that traverse the length of the rotor. Other weld configurations are possible as well, as are other attachment means, such as adhesives.

FIG. 6 shows the rotor 30 after the plates have been stacked and secured together.

Once the rotor plates 200 are secured together, such as by one of the above described welding processes, the rotor shaft 38 can be pressed onto the rotor 30 in a step 1008 to create the rotor assembly 5 shown at FIG. 1. In one embodiment, and as can be seen at FIGS. 7 and 8, the rotor shaft 38 is formed by a die set 540 to include a plurality of burrs 542 set at 90-degree increments about the output shaft 38. The height of the burrs 542 is set to interference fit with the central opening 212 in the plates 200 that form the rotor 30 when the shaft 38 is inserted therein. This permits power to be transferred from the rotor plates 200 to the shaft 38.

In a step 1010, a coating is applied to the rotor plates 200 of the rotor 30. In one embodiment, the coating is an abradable coating to allow tighter clearances between a pair of adjacent rotors 30, which may be especially useful in high temperature applications.

Rotor Assembly Applications

The above described rotor assembly 5 may be used in a variety of applications involving rotary devices. Two such applications are for use in a fluid expander 20 and a compression device 21 (e.g. a supercharger), as shown in FIG. 10. In one embodiment, the fluid expander 20 and compression device 21 are volumetric devices in which the fluid within the expander 20 and compression device 21 is transported across the rotors 30 without a change in volume. FIG. 10 shows the expander 20 and supercharger 21 being provided in a vehicle 10 having wheels 12 for movement along an appropriate road surface. The vehicle 10 includes a power plant 16 that receives intake air 17 and generates waste heat in the form of a high-temperature exhaust gas in exhaust 15. The power plant 16 may be an internal combustion (IC) engine or a fuel cell.

As shown, the expander 20 receives heat from the power plant exhaust 15 and converts the heat into useful work which can be delivered back to the power plant 16 to increase the overall operating efficiency of the power plant. As configured, the expander 20 includes housing 23 within which a pair of rotor assemblies 5 having intermeshed rotors 30 and shafts 38 are disposed. The expander 20 having rotor assemblies 5 can be configured to receive heat from the power plant 16 directly or indirectly from the exhaust.

One example of a fluid expander 20 that directly receives exhaust gases from the power plant 16 is disclosed in Patent Cooperation Treaty (PCT) International Application Number PCT/US2013/078037 entitled EXHAUST GAS ENERGY RECOVERY SYSTEM. PCT/US2013/078037 is herein incorporated by reference in its entirety.

One example of a fluid expander 20 that indirectly receives heat from the power plant exhaust via an organic Rankine cycle is disclosed in Patent Cooperation Treaty (PCT) International Application Publication Number WO 2013/130774 entitled VOLUMETRIC ENERGY RECOVERY DEVICE AND SYSTEMS. WO 2013/130774 is incorporated herein by reference in its entirety.

Still referring to FIG. 10, the compression device 21 is shown as being provided with housing 25 within which a pair of rotor assemblies 5 having intermeshed rotors 30 and shafts 38 are disposed. As configured, the compression device is driven by the power plant 16. As configured, the compression device 21 increases the amount of intake air 17 delivered to the power plant 16. In one embodiment, compression device 21 is a Roots-type blower of the type shown and described in U.S. Pat. No. 7,488,164 entitled OPTIMIZED HELIX ANGLE ROTORS FOR ROOTS-STYLE SUPERCHARGER. U.S. Pat. No. 7,488,164 is hereby incorporated by reference in its entirety.

Material Selection

Where the rotors 30 are disposed in a housing, such as housings 23 and 25, proper consideration must be given to material selection for the rotors and the housing in order to maintain desirable clearances between the rotors and housing. For example, improper material selection can result in a rotor that expands when heated by a working fluid (e.g. engine exhaust) into the interior wall of the housing, thereby damaging the rotor and housing and rendering the device inoperable. Proper selection of materials having appropriate relative coefficients of thermal expansion will result in a rotor that, in the expanded state, will not contact an also expanded housing and will maintain a minimum clearance between the rotors and housing for maximum efficiency across a broader range of temperatures. Also, as the rotors are more directly exposed to the working fluid (e.g. exhaust gases or a solvent used in a Rankine cycle) and the housing can radiate heat to the exterior, the rotors can be expected to expand to a greater degree than the housing. Accordingly, it is desirable to select a material for the rotors that has a coefficient of thermal expansion that is lower than a coefficient of thermal expansion of the housing.

Because the rotors can be provided with hollow lobes, a wider selection of materials having relatively low coefficients of thermal expansion may be used for the rotors because the resulting rotational inertia of a hollow-lobe rotor made from plates having a relatively high density can be the same or lower than the rotational inertia of a solid-lobe cast, machined, or laminated rotor made from a material having a relatively low density. For example, a stainless steel rotor with hollow lobes can be created with a rotational inertia generally similar to a solid-lobe aluminum rotor. As such, the disclosed rotor design allows a greater degree of material selection for the rotor which further widens the suitability of various materials for the housing.

In one particular application, the rotor assemblies 5 are used in an expander that receives exhaust gases from an internal combustion engine. In such an application, it is necessary that the rotor plates 200 be formed from a material that is suitable for operation at high exhaust gas temperatures, for example, stainless steel, tungsten, titanium, and carbon steel. As the rotors 30 can be provided with hollow lobes, these materials can be used in a high temperature expander application without resulting in a rotor 30 that has a rotational inertia that is too high for efficient operation. In one embodiment, stainless steel rotors are used in conjunction with an aluminum housing. As stainless steel has a lower coefficient of thermal expansion than aluminum, both the housing and the rotors will expand, but to a degree wherein each component expands to achieve clearances that allow for maximum efficiency. Of course, many other possibilities exist for rotor and housing materials based on desired performance criteria.

Rotor Assembly Method 2000

Referring to FIGS. 11-24, an example of a rotor assembly system and process 2000 in accordance with the disclosure is presented. It is noted that although the figures diagrammatically show steps in a particular order, the described procedures are not necessarily intended to be limited to being performed in the shown order. Rather at least some of the shown steps may be performed in an overlapping manner, in a different order and/or simultaneously. Also, the process shown in FIG. 11 is exemplary in nature and other steps or combinations of steps may be incorporated or altered without departing from the central concepts disclosed herein.

In a step 2002, a rotor assembly apparatus 300 is provided. As shown at FIG. 12, the rotor assembly apparatus includes an end plate 302 and a base plate 304 having a central opening 304 a. A mandrel 306 is also provided that extends from the base plate 302. Referring to FIG. 13, it can be seen that the base plate 304 is mounted over the mandrel 306 and abutting the end plate 302. As shown at FIG. 12, the mandrel has an index feature 308 including projections 308-1, 308-2, and 308-3. As shown, the projections 308 are provided along the length of the mandrel 306 and wrap about the mandrel 306 to form a helix such that a helical rotor 30 can be formed. However, it is noted that the projections 308 can be provided as straight projections running parallel to the length of the mandrel 306 such that a straight rotor 30 can be formed.

The index feature 308 is configured to engage with the index feature 214 of each rotor plate 200 such that projection 308-1 aligns with notch 214-1, projection 308-2 aligns with notch 214-2, and projection 308-3 aligns with notch 214-3 when the rotor plates 200 are stacked onto the mandrel 308. It is also noted that the index feature 308 can be provided with recesses or channels instead of projections to cooperate with corresponding tabs that would be provided on the rotor plates 200.

In the particular embodiment shown, the index feature 308 will impart a gradual helical twist for the assembled rotor 30 that will have a helix angle as defined by the index feature 308. The total twist angle of the rotor 30 can be defined by the total number of stacked rotor plates 200 and the helix angle defined by the index feature 308. In the embodiment shown, the helix angle defined by the mandrel indexing feature 308 is constant. However, the helix angle defined by the indexing feature 308 on the mandrel 306 may be increasing or decreasing along the length of the mandrel 306 such that a variable helix angle is imparted onto the stacked rotor plates 200.

In a step 2004, a plurality of rotor plates 200 in accordance with the above description are provided. In a step 2006, each of the provided rotor plates 200 is stacked onto the mandrel 306 such that the mandrel 306 extends through each of the central openings 212 of the rotor plates 200 and the index features 308, 214 are aligned. With reference to FIG. 14, it can be seen that a first rotor plate 200 a of the type shown at FIG. 11 is aligned with the mandrel 306. FIG. 15 shows a rotor plate 200 a of the shown in FIG. 5 installed onto the mandrel 306 with a second rotor plate 200 b of the type shown at FIG. 4 being aligned with the mandrel 306. FIG. 16 shows the second rotor plate 200 b being installed onto the mandrel 306 adjacent the first rotor plate 200 a. FIG. 17 shows the process at the point where a plurality of second rotor plates 200 b have been stacked together with another two first rotor plates 200 a resting on the top of the stack for a total of 125 stacked rotor plates 200. Because of the helical index feature 308 on the mandrel 306, it can be seen that each rotor plate 200 is slightly offset from the adjacent rotor plate about the central axis X to form a helical rotor. As configured, each of the stacked rotor plates 200 is adjacent to another rotor plate 200 such that no gap exists between the adjacent plates.

It is noted that many configurations of stacked rotor plates 200 are possible using assembly method 2000. In the example embodiment shown, the stack could include closed-lobe rotor plates with indexing holes of the type shown in FIG. 5 at each end with hollow-lobe rotor plates of the type shown in FIG. 4 there between. In another embodiment, the stack could consist entirely of hollow-lobe rotor plates of the type shown in FIG. 4. Alternatively, the stack could include closed-lobe rotor plates of the type shown in FIG. 2 at each end with hollow-lobe rotor plates of the type shown in FIG. 4 there between. In even yet another configuration, the stack could include alternating hollow-lobe rotor plates with solid-lobe rotor plates. Alternatively, the stack could include a majority of the plates as being hollow-lobe rotor plates with solid-lobe rotor plates being inserted incrementally throughout the stack, for example, every tenth plate could be a solid-lobe rotor plate with the remaining plates being a hollow-lobe type.

In a step 2008, the rotor plates 200 are secured together as shown at FIG. 18. In one embodiment, the rotor plates 200 are initially secured together by mounting a top plate 310 over the mandrel 306 and securing the top plate 310 with a bushing 312 and nut 314. When the nut is tightened, a compression force is exerted on the stacked rotor plates via the top plate 310, the bottom plate 304, and the mandrel 306. The stacked rotor plates 200 can then be further secured together, for example by welding. In one example, the plates 200 are secured together by laser welding. In another example, the rotor plates 200 can be welded together in a vacuum or continuous belt furnace. In an alternative, the plates 200 can be plated and resistive-welded together. In one embodiment, the rotor plates 200 are secured with welds that extend along the rotor plate tips 203 and along each side of the rotor lobes 202 for a total of nine helical welds that traverse the length of the rotor. Other weld configurations are possible as well, as are other attachment means, such as adhesives.

Once the rotor plates 200 are secured together, such as by one of the above described welding processes, the rotor plates 200 and mandrel 306 can be removed from the end plate 302, base plate 304, and top plate 306, as shown at FIG. 19. In a step 2010, the mandrel 306 is extracted from the secured rotor plates 200 with the rotor assembly apparatus 300 reconfigured as an extraction tool wherein first end plate 302 is secured to a second end plate 320 via a plurality of connecting rods 322. A push rod 324 can then be provided that forces the mandrel through the stacked rotor plates 200 to result in the stacked rotor plate assembly shown in FIG. 21.

In a step 2012, the rotor shaft 38 is pressed into the stacked rotor plate assembly to create an assembled rotor 30, as shown at FIG. 1. In a step 2014, a coating is applied to the rotor plates 200 of the rotor 30. In one embodiment, the coating is an abradable coating to allow tighter clearances between two adjacent rotors 30 which may be especially useful in high temperature applications. In a step 1016, the rotor assembly 5 is balanced. In one embodiment, the rotor assembly 5 is balanced by selectively removing material from one or more of the lobes of one or more rotor plates 200.

While the best modes for carrying out the many aspects of the present teachings have been described in detail, those familiar with the art to which these teachings relate will recognize various alternative aspects for practicing the present teachings that are within the scope of the appended claims. 

What is claimed is:
 1. A method of making a laminated rotor, the method comprising the steps of: a. providing a plurality of rotor plates, each of the plates having a plurality of lobes extending radially away from a central opening and a first indexing feature; b. providing a mandrel having a second indexing feature; c. stacking each of the rotor plates onto the mandrel such that the mandrel extends through the central opening of each plate and such that the rotor plate first indexing feature is aligned with the mandrel second indexing feature; d. securing the rotor plates together; e. removing the mandrel from the rotor plates; and f. inserting a shaft into the central openings of the rotor plates.
 2. The method of making a laminated rotor of claim 1, wherein the step of providing a plurality of rotor plates includes providing at least some of the rotor plates with openings in the rotor plate lobes.
 3. The method of making a laminated rotor of claim 1, wherein the step of securing the rotor plates together includes welding the rotor plates together.
 4. The method of making a laminated rotor of claim 1, further including the step of burring the shaft before the step of inserting the shaft into the central openings of the rotor plates.
 5. The method of making a laminated rotor of claim 1, wherein the step of inserting a shaft is performed after the step of securing the rotor plates together.
 6. The method of making a laminated rotor of claim 1 further including the step of forming each of the plurality rotor plates by one of stamping, fine blanking, laser cutting, and water jet cutting.
 7. The method of making a laminated rotor of claim 1, wherein the step of providing a mandrel includes providing a mandrel with the second indexing feature having a plurality of protrusions extending along a length of the mandrel.
 8. The method of making a laminated rotor of claim 7, wherein the step of providing a mandrel includes providing a mandrel with the second indexing feature having a plurality of helical protrusions.
 9. The method of making a laminated rotor of claim 8, wherein the step of providing a mandrel includes providing a mandrel with the second indexing feature having three helical protrusions.
 10. The method of making a laminated rotor of claim 8, wherein the step of providing a plurality of rotor plates includes providing a plurality of rotor plates having a plurality of recesses forming the first indexing feature.
 11. The method of making a laminated rotor of claim 10, wherein the steps of providing a mandrel and providing a plurality of rotor plates includes providing a mandrel with a number of protrusions that is equal to a number of recesses provided on each rotor plate.
 12. A rotor assembly comprising: a. a plurality of rotor plates, each including: i. a first side and a second opposite side separated by a first thickness; ii. a central opening extending between the first and second sides; iii. a plurality of lobes extending away from the central opening; iv. an indexing feature including at least one recess extending from the central opening; and b. a shaft extending through the central opening of each of the plurality of rotor plates; c. wherein the plurality of rotor plates are stacked and secured together to form the rotor assembly such that at least one of the first and second sides of one rotor plate is adjacent to and in contact with at least one of the first and second sides of another rotor plate.
 13. The rotor assembly of claim 12, wherein the rotor plates are rotated with respect to each other to form a helical rotor.
 14. The rotor assembly of claim 13, wherein each of the plurality of rotor plates includes first, second, and third lobes that are radially spaced apart by an equal angular degree.
 15. The rotor assembly of claim 14, wherein each of the plurality of rotor plates further includes a fourth lobe, wherein the first, second, third, and fourth lobes are radially spaced apart by an equal angular degree.
 16. The rotor assembly of claim 13, wherein the helical rotor has an overall length that is generally equal to the sum of the first thicknesses of the plurality of stacked rotor plates.
 17. The rotor assembly of claim 12, wherein each of the plurality of lobes includes a lobe opening.
 18. The rotor assembly of claim 12, wherein each of the rotor plates is formed from a metal material.
 19. The rotor assembly of claim 18, wherein each of the rotor plates is formed from stainless steel.
 20. The rotor assembly of claim 18, wherein the rotor plates are secured together by welding. 